Part D - Materials and Construction

4.19 Materials

Goal

To ensure that the cargo containment system, primary and secondary barriers, the thermal insulation, adjacent ship structure and other materials in the cargo containment system are constructed from materials of suitable properties for the conditions they will experience, both in normal service and in the event of failure of the primary barrier, where applicable.

4.19.1 Materials forming ship structure

4.19.1.1 To determine the grade of plate and sections used in the hull structure, a temperature calculation shall be performed for all tank types when the cargo temperature is below -10°C. The following assumptions shall be made in this calculation:

• .1 the primary barrier of all tanks shall be assumed to be at the cargo temperature;

• .2 in addition to .1, where a complete or partial secondary barrier is required, it shall be assumed to be at the cargo temperature at atmospheric pressure for any one tank only;

• .3 for worldwide service, ambient temperatures shall be taken as 5°C for air and 0ºC for seawater. Higher values may be accepted for ships operating in restricted areas and, conversely, lower values may be fixed by the Administration for ships trading to areas where lower temperatures are expected during the winter months;

• .4 still air and seawater conditions shall be assumed, i.e. no adjustment for forced convection;

• .5 degradation of the thermal insulation properties over the life of the ship due to factors such as thermal and mechanical ageing, compaction, ship motions and tank vibrations, as defined in 4.19.3.6 and 4.19.3.7, shall be assumed;

• .6 the cooling effect of the rising boil-off vapour from the leaked cargo shall be taken into account, where applicable;

• .7 credit for hull heating may be taken in accordance with 4.19.1.5, provided the heating arrangements are in compliance with 4.19.1.6;

• .8 no credit shall be given for any means of heating, except as described in 4.19.1.5; and

• .9 for members connecting inner and outer hulls, the mean temperature may be taken for determining the steel grade.

The ambient temperatures used in the design, described in this paragraph, shall be shown on the International Certificate of Fitness for the Carriage of Liquefied Gases in Bulk required in 1.4.4.

LR 4.19-01 The minimum temperatures used in determining the required grade of materials are to be calculated using the boundary conditions given in 4.19.1.1. Where a higher or lower ambient temperature is to be used in accordance with 4.19.1.1.3, this is to be included in the class notation. The revised ambient temperatures are to be considered when determining the required hull material grades, both within and outside the cargo area.

LR 4.19-02 The temperatures of members connecting the inner and outer hulls are to be obtained from the calculations.

LR 4.19-03 The heat balance method may be used to carry out the temperature calculations required in 4.19.1.1.

4.19.1.2 The shell and deck plating of the ship and all stiffeners attached thereto shall be in accordance with recognized standards. If the calculated temperature of the material in the design condition is below -5°C due to the influence of the cargo temperature, the material shall be in accordance with table 6.5.

LR 4.19-04 The material of the hull structure, other than that forming part of, or adjoining, the cargo containment system, is to comply with the requirements given in LR 6.4-01 and subsequent paragraphs.

4.19.1.3 The materials of all other hull structures for which the calculated temperature in the design condition is below 0°C, due to the influence of cargo temperature and that do not form the secondary barrier, shall also be in accordance with table 6.5. This includes hull structure supporting the cargo tanks, inner bottom plating, longitudinal bulkhead plating, transverse bulkhead plating, floors, webs, stringers and all attached stiffening members.

4.19.1.4 The hull material forming the secondary barrier shall be in accordance with table 6.2. Where the secondary barrier is formed by the deck or side shell plating, the material grade required by table 6.2 shall be carried into the adjacent deck or side shell plating, where applicable, to a suitable extent.

4.19.1.5 Means of heating structural materials may be used to ensure that the material temperature does not fall below the minimum allowed for the grade of material specified in table 6.5. In the calculations required in 4.19.1.1, credit for such heating may be taken in accordance with the following:

• .1 for any transverse hull structure;

• .2 for longitudinal hull structure referred to in 4.19.1.2 and 4.19.1.3 where colder ambient temperatures are specified, provided the material remains suitable for the ambient temperature conditions of +5°C for air and 0°C for seawater with no credit taken in the calculations for heating; and

• .3 as an alternative to .2, for longitudinal bulkhead between cargo tanks, credit may be taken for heating, provided the material remain suitable for a minimum design temperature of -30°C, or a temperature 30°C lower than that determined by 4.19.1.1 with the heating considered, whichever is less. In this case, the ship's longitudinal strength shall comply with SOLAS regulation II-1/3-1 for both when those bulkhead(s) are considered effective and not.

4.19.1.6 The means of heating referred to in 4.19.1.5 shall comply with the following requirements:

• .1 the heating system shall be arranged so that, in the event of failure in any part of the system, standby heating can be maintained equal to not less than 100% of the theoretical heat requirement;

• .2 the heating system shall be considered as an essential auxiliary. All electrical components of at least one of the systems provided in accordance with 4.19.1.5.1 shall be supplied from the emergency source of electrical power; and

• .3 the design and construction of the heating system shall be included in the approval of the containment system by the Administration or recognized organization acting on its behalf.

4.19.2 Materials of primary and secondary barriers

LR 4.19-06 The specification and plans of the cargo containment system including the insulation are to be submitted for approval. The materials used are to be approved by LR.

4.19.2.1 Metallic materials used in the construction of primary and secondary barriers not forming the hull, shall be suitable for the design loads that they may be subjected to, and be in accordance with, table 6.1, 6.2 or 6.3.

4.19.2.2 Materials, either non-metallic or metallic but not covered by tables 6.1, 6.2 and 6.3, used in the primary and secondary barriers may be approved by the Administration or recognized organization acting on its behalf, considering the design loads that they may be subjected to, their properties and their intended use.

4.19.2.3 Where non-metallic materials, including composites, are used for, or incorporated in the primary or secondary barriers, they shall be tested for the following properties, as applicable, to ensure that they are adequate for the intended service:

• .1 compatibility with the cargoes;

• .2 ageing;

• .3 mechanical properties;

• .4 thermal expansion and contraction;

• .5 abrasion;

• .6 cohesion;

• .7 resistance to vibrations;

• .8 resistance to fire and flame spread; and

• .9 resistance to fatigue failure and crack propagation.

4.19.2.4 The above properties, where applicable, shall be tested for the range between the expected maximum temperature in service and +5°C below the minimum design temperature, but not lower than -196°C.

4.19.2.5.1 Where non-metallic materials, including composites, are used for the primary and secondary barriers, the joining processes shall also be tested as described above.

4.19.2.5.2 Guidance on the use of non-metallic materials in the construction of primary and secondary barriers is provided in appendix 4.

4.19.2.6 Consideration may be given to the use of materials in the primary and secondary barrier, which are not resistant to fire and flame spread, provided they are protected by a suitable system such as a permanent inert gas environment, or are provided with a fire-retardant barrier.

4.19.3 Thermal insulation and other materials used in cargo containment systems

4.19.3.1 Load-bearing thermal insulation and other materials used in cargo containment systems shall be suitable for the design loads.

4.19.3.2 Thermal insulation and other materials used in cargo containment systems shall have the following properties, as applicable, to ensure that they are adequate for the intended service:

• .1 compatibility with the cargoes;

• .2 solubility in the cargo;

• .3 absorption of the cargo;

• .4 shrinkage;

• .5 ageing;

• .6 closed cell content;

• .7 density;

• .8 mechanical properties, to the extent that they are subjected to cargo and other loading effects, thermal expansion and contraction;

• .9 abrasion;

• .10 cohesion;

• .11 thermal conductivity;

• .12 resistance to vibrations;

• .13 resistance to fire and flame spread; and

• .14 resistance to fatigue failure and crack propagation.

LR 4.19-07 Details of the extent of ageing of the insulation material used in the cargo containment system are to be submitted to LR for consideration, see also 4.19.3.6 and LR 4.19-06.

4.19.3.3 The above properties, where applicable, shall be tested for the range between the expected maximum temperature in service and 5°C below the minimum design temperature, but not lower than -196°C.

LR 4.19-08 In addition to the requirements given in 4.19.3.2, fatigue and crack propagation properties for insulation in membrane systems are also to be submitted. Insulation materials are to be approved by LR. Where applicable, these requirements also apply to any adhesive, sealers, vapour barriers, coatings or similar products used in the insulation system, any material used to give strength to the insulation system, components used to hold the insulation in place and any non-metallic membrane materials. Such products are to be compatible with the insulation.

4.19.3.4 Due to location or environmental conditions, thermal insulation materials shall have suitable properties of resistance to fire and flame spread and shall be adequately protected against penetration of water vapour and mechanical damage. Where the thermal insulation is located on or above the exposed deck, and in way of tank cover penetrations, it shall have suitable fire resistance properties in accordance with recognized standards or be covered with a material having low flame-spread characteristics and forming an efficient approved vapour seal.

4.19.3.5 Thermal insulation that does not meet recognized standards for fire resistance may be used in hold spaces that are not kept permanently inerted, provided its surfaces are covered with material with low flame-spread characteristics and that forms an efficient approved vapour seal.

4.19.3.6 Testing for thermal conductivity of thermal insulation shall be carried out on suitably aged samples.

LR 4.19-09 Proposals for the thermal conductivity tests of aged samples of the insulation are to be submitted by the designer and/or insulation makers, and are to be agreed with LR based on the physical and chemical characteristics of the insulation.

4.19.3.7 Where powder or granulated thermal insulation is used, measures shall be taken to reduce compaction in service and to maintain the required thermal conductivity and also prevent any undue increase of pressure on the cargo containment system.

LR 4.19-10 Particular attention is to be paid to the cleaning of the steelwork prior to the application of the insulation. Where insulation is to be foamed or sprayed in situ, the minimum steelwork temperature at the time of application is to be indicated in the specification in addition to environmental conditions.

4.20 Construction processes

To define suitable construction processes and test procedures in order to ensure, as far as reasonably practical, that the cargo containment system will perform satisfactorily in service in accordance with the assumptions made at the design stage.

4.20.1 Weld joint design

LR 4.20-02 The requirements of this Section are to be applied in association with the relevant Chapters of the Rules for Ships. For welding joint details of pressure vessels, see Pt 5, Ch 10,14 of the Rules for Ships.

4.20.1.1 All welded joints of the shells of independent tanks shall be of the in-plane butt weld full penetration type. For dome-to-shell connections only, tee welds of the full penetration type may be used depending on the results of the tests carried out at the approval of the welding procedure. Except for small penetrations on domes, nozzle welds shall also be designed with full penetration.

LR 4.20-03 In the context of 4.20.1.1, small penetrations may generally be considered as penetrations of diameter not greater than 50 mm. Penetrations of diameter not greater than 150 mm may also be considered as being small, provided the service temperature is not lower than -110ºC, and the tank design pressure is not greater than 0,07MPa.

LR 4.20-04 In accordance with 4.20.1.1 full penetration T-butt welds may be used for dome-to-shell connections. Full penetration T-butt welds between shell and longitudinal bulkhead for bi-lobe tanks may also be accepted subject to agreement from the National Administration.

LR 4.20-05 Regulation 4.20.1.1 is applicable to independent tanks of type A or type B, primarily constructed of plane surfaces. This includes the tank corners, which are constructed using bent plating aligned with the tank surfaces and connected with in-plane welds.

LR 4.20-06 In the context of regulation 4.20.1.1, the applicability of the expression ‘For dome-to-shell connections only’ is clarified as follows:

• Welded corners (i.e. corners made of weld metal) shall not be used in the main tank shell construction, i.e. corners between the shell side (sloped plane surfaces parallel to hopper or top side inclusive, if any) and bottom or top of the tank, and between the tank end transverse bulkheads and the bottom, top or shell sides (sloped plane surfaces inclusive, if any) of the tank. Instead, tank corners which are constructed using bent plating aligned with the tank surfaces and connected with in-plane welds, are to be used.
• Tee welds can be accepted for other localised constructions of the shell such as suction well, sump, dome, etc. where tee welds of full penetration type shall also be used.

4.20.1.2 Welding joint details for type C independent tanks, and for the liquid-tight primary barriers of type B independent tanks primarily constructed of curved surfaces, shall be as follows:

• .1 all longitudinal and circumferential joints shall be of butt welded, full penetration, double vee or single vee type. Full penetration butt welds shall be obtained by double welding or by the use of backing rings. If used, backing rings shall be removed except from very small process pressure vessels. Other edge preparations may be permitted, depending on the results of the tests carried out at the approval of the welding procedure; and

• .2 the bevel preparation of the joints between the tank body and domes and between domes and relevant fittings shall be designed according to a standard acceptable to the Administration or recognized organization acting on its behalf. All welds connecting nozzles, domes or other penetrations of the vessel and all welds connecting flanges to the vessel or nozzles shall be full penetration welds.

LR 4.20-07 In the context of regulation 4.20.1.2, the applicability of the expression ‘Other edge preparations’ is clarified as follows:

• Cruciform full penetration welded joints in a bi-lobe tank with centreline bulkhead can be accepted for the tank structure construction at tank centreline welds with bevel preparation subject to the approval of LR, based on the results of the tests carried out at the approval of the welding procedure (see Figure LR 4.1 Cruciform full penetration weld).

4.20.1.3 Where applicable, all the construction processes and testing, except that specified in 4.20.3, shall be done in accordance with the applicable provisions of chapter 6.

4.20.2 Design for gluing and other joining processes

The design of the joint to be glued (or joined by some other process except welding) shall take account of the strength characteristics of the joining process.

4.20.3 Testing

4.20.3.1 All cargo tanks and process pressure vessels shall be subjected to hydrostatic or hydropneumatic pressure testing in accordance with 4.21 to 4.26, as applicable for the tank type.

4.20.3.2 All tanks shall be subject to a tightness test which may be performed in combination with the pressure test referred to in 4.20.3.1.

4.20.3.3 Requirements with respect to inspection of secondary barriers shall be decided by the Administration or recognized organization acting on its behalf in each case, taking into account the accessibility of the barrier (see 4.6.2).

4.20.3.4 The Administration may require that for ships fitted with novel type B independent tanks, or tanks designed according to 4.27 at least one prototype tank and its supporting structures shall be instrumented with strain gauges or other suitable equipment to confirm stress levels. Similar instrumentation may be required for type C independent tanks, depending on their configuration and on the arrangement of their supports and attachments.

4.20.3.5 The overall performance of the cargo containment system shall be verified for compliance with the design parameters during the first full loading and discharging of the cargo, in accordance with the survey procedure and requirements in 1.4 and the requirements of the Administration or recognized organization acting on its behalf. Records of the performance of the components and equipment essential to verify the design parameters, shall be maintained and be available to the Administration.

LR 4.20-08 The overall performance of the cargo containment system is to be verified for compliance with the design parameters during initial acceptance cargo trials. The initial trials are to be witnessed by LR’s Surveyors, and are to demonstrate that the system is capable of being inerted, cooled, loaded and discharged in a satisfactory manner, and that all safety devices function correctly. The temperature at which these tests are carried out is to be at or near the minimum cargo temperature. Where refrigeration plant is fitted, its operation is to be demonstrated to the Surveyors. Records of the plant performance taken during the first loaded voyage at minimum temperature are to be submitted. The above tests may be carried out in conjunction with the vessel’s normal trading commitments. Normal voyage logs of plant performance are to be maintained for examination by the Surveyors when requested.

4.20.3.6 Heating arrangements, if fitted in accordance with 4.19.1.5 and 4.19.1.6, shall be tested for required heat output and heat distribution.

4.20.3.7 The cargo containment system shall be inspected for cold spots during, or immediately following, the first loaded voyage. Inspection of the integrity of thermal insulation surfaces that cannot be visually checked shall be carried out in accordance with recognized standards.